In 3GPP (3rd Generation Partnership Project) which is a project aiming to standardize a mobile communication system, the introduction of Device to Device (D2D) communication is discussed as a new function after Release 12 (see Non Patent Document 1).
In D2D communication, a plurality of proximal user terminals perform direct device-to-device communication without passing through a network. On the other hand, in cellular communication which is normal communication in a mobile communication system, a user terminal performs communication via a network.
Further, it is assumed that scheduling for assigning a radio resource used for transmitting and receiving user data in D2D communication includes a case where a user terminal performing the D2D communication takes an initiative to perform the scheduling as well as a case where a base station included in a network takes an initiative to perform the scheduling. As a result of the user terminal performing the D2D communication assigning the radio resource by the user terminal itself, it is possible to reduce a load of the base station.